1. Field of the Invention
This invention relates to the coating of objects having exterior surfaces of revolution. This invention also relates to the printing of substantially cylindrical containers including drawn and ironed containers having integral bottom and side walls.
Printing machines of this type generally comprise a container feeding system supplying containers to a rotary drum carrying a plurality of mandrels at a plurality of angular positions around the mandrel drum. After the containers have been placed on the mandrels, the mandrels rotate to a position adjacent an offset printing blanket which is supplied by one or more printing cylinders. As the containers carried by the mandrels contact the printing blanket, print is transferred to the container. The containers then move to and engage an adjacent coater before being removed from the mandrels and placed on an outfeed conveyor.
In the ideal case, each mandrel will carry a properly seated container before reaching the printing blanket and the coater. However, certain malfunctions can and do occur in the feeding mechanism which will result in the absence of a container on the mandrel or the improper seating of a container on a mandrel. In either case, it is undesirable to have the mandrel reach the vicinity of the printing blanket and the coater since the printing and the coating may be transferrred to the mandrel itself. In the case of a missing container, the entire mandrel will be printed and coated. In the case of an improperly seated container, at least a portion of the mandrel will be printed and coated. This in turn will result in the contamination of the interior of the next container to be fed to and placed on that particular mandrel.
2. Prior Art
The foregoing problems arising out of a feeding malfunction have been recognized in the prior art. The principal approach in solving this problem has involved relative movement between the mandrel drum and the printing blanket and/or coater. When the absence of a container or the improper seating of a container is detected by suitable means such as a pneumatic detector or an electrical switch, the rotary mandrel and the printing blanket or coater have been separated momentarily to allow the mandrel of the missing or improperly seated container to pass without engaging the printing blanket and coater. In general, this involves movement of the rotary drum rather than the heavier and larger printing blanket and/or coater. Nevertheless, the size and weight of the rotary drum imposes severe limitations on the speed with which the drum can be moved from and to a position adjacent to the printing blanket and coater. This in turn imposes limitations on the output of the printing and coating machine requiring the use of more than one printing and coating machine to supply a high speed container production line or, in the alternative, slowing down the high speed container line which is of course very costly from a production standpoint. U.S. Pat. No. 3,227,070 - Brigham et al described the foregoing approach to the problem.
Another approach to the problem is shown in U.S. Pat. No. 3,496,863 - Cvacho et al. This involves the use of an adjustable cam track which cams the mandrel support mechanism radially inwardly when a feeding malfunction is detected by a suitable mechanism. When there is no feeding malfunction the cam moves the cam followers of the mandrel support mechanism through a path leading to contact between the containers carried by the mandrels and the printing blanket. In the absence of the container on a mandrel or the improper seating of a container on a mandrel, a portion of the cam guiding the cam followers is pivoted radially inwardly to force the cam follower and the associated mandrel radially inwardly away from the printing blanket. A similar camming motion occurs at the coater as the mandrel with the missing or improperly seated container approaches. This approach which involves movement of the mandrel cam is also somewhat slow since sufficient time must be left to allow the cam to move back to the normal position before the next mandrel carrying a properly seated container reaches the movable portion of the mandrel cam.
U.S. Pat. No. 3,613,571 - Russell et al discloses another approach for preventing the printing or coating of a mandrel in a high speed printing machine. This involves the use of pneumatic detectors which sense the absence of a container on a mandrel and then actuate a linking mechanism so as to rotate a mandrel supporting arm inwardly away from a printing blanket as a cam follower moves along the mandrel camming surface. Thus, the cam follower always remains in contact with the camming surface but the camming surface provides a different effect when a container is absent.
In the foregoing systems, electrical switches or fluid actuated detectors are utilized for sensing the absence or improper seating of a container on a mandrel. The detectors in turn actuate a separate mechanism for preventing contact between the mandrels and the printing blanket. Generally, a detection system of this type which involves a pneumatic or electrical transducer is less reliable than a positive and direct mechanical detection mechanism.